It is the best for now. Session manager was even better but the important things are:

it is open source;
it can import sessions saved by session manager.

In fact too many times I had to lose all my sessions after moving to a new "session manager" addon.

My question is, what for is the permission for downloading files and READ AND MODIFY download history, on top of that, required. That's sneaky and suspicious.
Yeah... That simultaneous loading of all tabs is a disaster...
I'd also vote for a "saved sessions list compact view" option. Like one-two text lines without much space-eating decorations.
Anyway, thank you for active development and support for Tree Style Tabbar! Your addon is indispensable, irreplaceable and a kind of a savior these days!

I had to get this extension as a replacement for "Session Manager" as the new Firefox doesn't support that one anymore. It's a 5 star program and I absolutely hate giving anything less than five stars...but the only reason why I have is because for work I have tabs open to local html files I created myself, and every time I restore my tabs with this extension it only opens up web pages from the actual web and never opens up my local html files that I need which makes me have to go and open them up one by one. I could do it myself, but I got this extension to keep from having to take time to do that so I don't mix them up and can start working right away. Also, it doesn't ever open all the tabs when there is more than one window saved, usually meaning I have to open up all the tabs myself in the second window as well. Hopefully it can get updated soon. It's DEFINITELY much faster than Session Manager, but I need it to save and open all the tabs ^_^

56まで使えたアドオンFEBEのように、アドオンの設定やテーマの画像、ブックマークデータなど全てのデータを一括バックアップできるようになると、Firefoxを再インストールしたり、新しく使う際にとても助かります。
お手数ですが、ご検討よろしくお願いいたします。

I had to find a replacement for the old Session Manager, which worked well until FF57, and then not at all.
I give kudos to the author of this add on for going to the trouble to provide an extension that substitutes for the legacy Session Manager in part. If it can duplicate more of the functionality of the older extension, it would rate FIVE stars for sure. But I thank the author and rate four stars at this time.
There are issues which I hope can be dealt with as this extension develops:
- I had a large 196 tab session saved, which Tab Session Manager shows OK, but when I try to open the session, only a portion of them do load. There seems to be a limit here. It would be nice if there was not.
- I note the latest version 1.5 has an option to Export the tabs (I presume as a list of links), but I haven't located this feature. This would enable me to sort through the 196 tabs mentioned in the previous point, so I hope I can find it - FOUND IT! Cool. Oh, but it only exports as a .json file which is not so useful. Update: but it is not to hard to manipulate the file with Notepad++ using "windowId": value to extract the tabs from a particular session.
- I echo the statement of "Anonymous user 8e0130" who asked "Is there anyway to have it not load non-active tabs?"
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This addon used to work perfectly, but unfortunately won't load sessions anymore

There's still a lot of work to do... but just to be able to import and open my old session manager's sessions (under ubuntu find them under ~/.mozilla/firefox/*some cryptic-key*.default/sessions/*here they are!!!*, which I though I'd never see again under firefox 57+, has just made me sooooo happy!!! So I just wanted to say THANKS!!!! a) For my sessions back, b) for giving us an alternative to keep going.

And don't listen to all those stupid comments of people, who probably think, open-source code just falls down from trees or something...

I give this add-on 5 starts, just because it recovered all my sessions from session manager after the update to FF57. Sure, it's not the same yet, but I guess the creator knows what functionalities he needs to add.

ウインドウのサイズ ページの表示位置 を保存できるように あれと寸分違わない機能が欲しい

It’s almost there just needs four things

First the ability to sort sessions alphabetically.

Second ask for conformation when deleting a session (one miss click and it could be gone that’s not good).

Third don’t activate every window when opening a session, only open the link when the user clicks the tab.

Forth when you open the tab manger window it should default to whatever view the user had last. So if the user last had “User Saved” clicked and it was set to sort by oldest it should stay like that every time you open the window until it is changed (even after closing and reopening Firefox). Or at the very lest you should be able to set the default view in the settings.

The Firefox community is counting on you plz i created an account just to write this.

This has been good so far. Does exactly what it said it will do. Looking forward to seeing the new features the developer is working on.

For all the negative reviewers, please read the description carefully, and understand that not all features can be imported into extensions. Stop punishing the developers of new add-ons trying to make things work in FF57 for things out of their control, its counter-productive.

Very simple and easy to use. Found a work around for not supporting the import of Session Manager files, but I really appreciate that they can now be imported.
I would like the option to automatically load the last session when Firefox is started. Otherwise I can't think of anything else I need from this addon.

As others have said, there is a bug when restoring sessions, it doesn't restore all windows or tabs. As this is the only functionality of this add on I can't give more than 1 star.

Edit - The latest update has fixed the issue above and also added lazy load.

It works well,I don't know why many poeple diss it.If there is a litte weakness that 's it open multiple windows for each saved session